Constraint-Induced Movement therapy or CI therapy is a behavioral approach to neurorehabilitation based on a program of neuroscience experiments conducted with deafferented monkeys. Over the last 20 years, a large body of evidence has accumulated to support the efficacy of CI therapy for rehabilitating hemiparetic arm use in individuals with chronic stroke. Given the persuasive evidence for its efficacy to date, other research questions have risen to the forefront. How cost-effective is CI therapy? What are optimal training and other treatment parameters? What patient characteristics moderate the effects of CI therapy? The papers gathered in this special issue address many of these topics. © 2006 - IOS Press and the authors. All rights reserved.